Staying Safe When Air Quality Is Poor

The following is a letter coauthored by John Balmes, MD, Kirk R. Smith, PhD, and Ajay Pillarisetti, PhD, in November 2018 during the devastating Camp Fire wildfire in Northern California, which led to dangerously high levels of particulate pollutants in the air in the San Francisco Bay Area, including Berkeley. All three authors are experts in air pollution and faculty members at the School of Public Health (SPH) at UC Berkeley; Drs. Balmes and Smith are also on the Editorial Board of Berkeley Wellness. They wrote the letter, reprinted with their permission, in response to a request from the SPH Interim Dean to provide the school community with advice for staying as safe as possible during this environmental crisis.

Dear SPH Community:

Dean [William] Dow has asked that we reach out to you to share our advice about the health impacts of the poor air quality that we have experienced in the Bay Area for the past week due to the smoke from the Camp Fire in Butte County. All of us have been studying the health effects of air pollution for many years and John is a pulmonary physician who treats patients at Zuckerberg San Francisco General Hospital.

Although woodsmoke contains a mixture of pollutants, air pollution scientists focus on the fine particulate matter as the best indicator of health risk. Particularly important are thought to be particles smaller than 2.5 microns in diameter (PM2.5). (To put that in perspective, the diameter of a human hair is ~60 microns.) Here in the Bay Area over 150 miles south of the Camp Fire, it is really only PM2.5 that we are concerned about. When inhaled, PM2.5 can deposit in the deep lung, where it can cause local injury and inflammation. The U.S. EPA National Ambient Air Quality Standard—a rigorous guideline set for protection of public health—for a 24-hour average exposure is 35 micrograms per cubic meter (µg/m3); a similar guideline value from the World Health Organization (WHO) is 25 µg/m3. PM2.5 concentrations have been elevated since last Friday (Nov. 9), but yesterday (Nov. 15) the concentration reached over 200 µg/m3 for one hour, although the average for the day was about 150 µg/m3. Mid-day on Friday the 16th, the level at the Aquatic Park regulatory monitor, the nearest monitor to campus, was again above 200 µg/m3.

The EPA and the Bay Area Air Quality Management District use what is called the Air Quality Index (AQI) to provide the public with warning about health risks from poor air quality with qualitative words and colors: good is green, moderate is orange, etc. [Editor's note: You can check your local AQI at AirNow.gov.) AQI over 200, which is equivalent to PM2.5 over 150 µg/m3, is the start of the “very unhealthy” (purple) level. AQI is based on non-linear comparisons of the actual level with the standard, i.e. 35 µg/m3 for 24 hours. (More later about these metrics and comparisons to other parts of the world.)

What are the health risks when the air quality is this bad? People with preexisting respiratory disease (such as asthma) and cardiovascular disease (such as coronary artery disease) are at risk of exacerbations. Even healthy people are at increased risk of developing acute lower respiratory tract infections (bronchitis or pneumonia, for example) when the air quality is hazardous.

What do we recommend when the air quality is in the unhealthy zone? The primary recommendation is to reduce exposure. This means staying indoors as much as possible with windows closed and any ventilation system turned to recirculation mode or off so that outdoor air is not brought indoors. Under these conditions, nearly any building acts to cut the outdoor levels by 20-40 percent. Modern buildings with mechanical air circulation systems often have filtersthat further cut these levels. We are doing measurements, but it seems our new building, Berkeley Way West, is able to cut the outside levels by a factor of four or so.

There are portable air purifiers available that clean the air in any room where they are placed, but only if big leaks to the outside are sealed, i.e. little outside air is brought in, and, importantly, the HEPA filter in them is changed when it saturates. They should also be big enough to provide sufficient clear air to handle the size of the room, the so-called CADR (clean air delivery rate), a metric required to be noted on the box. Of course, there should be no solid fuel combustion sources inside the house: cigarettes, fireplaces, incense, or candles, for example. Preferably, ever.

If you have to go outdoors, wear a N95 or N100 mask. An N95 mask is 95 percent efficient at filtering particles that are 0.3 micron in size, and an N100 is 100 percent efficient. Both mask types must fit properly over your nose and mouth to be effective. These masks are certified by the National Institute for Occupational Safety and Health (NIOSH), the agency within the CDC responsible for protecting worker health. They come in three sizes—S, M, and L—for adults. Make sure to get the one that best fits your face. Unfortunately, N95 or N100 masks cannot be recommended for young children because they are not made to fit a small child’s face. They also are not as effective when worn over a beard because of the lack of a seal. Importantly, they must fit very tightly, to the point of being uncomfortable, to work well.

While the current bad air quality makes people justifiably concerned about their health, it is unlikely that there will be long-term consequences for people in good health without preexisting respiratory or cardiovascular disease. People with such health problems should be careful to keep their exposure to the wildfire smoke as low as possible.